<p style="text-align: justify;"><strong>Objectives. </strong>At the moment, there are extremely insufficient diagnostic tools suitable for examining the communicative sphere of children with severe complicated forms of autism, and recorded practical experience of their use in organizing psychological and pedagogical support for such children. The purpose of the study is to test the diagnostic tool &ldquo;Communication Matrix&rdquo; in working with a child of primary school age with a severe complicated form of autism (autism spectrum disorder (ASD), moderate intellectual disability, systemic speech under-development, visual impairment, atopic dermatitis), who was learning the skills of communication using the PECS image exchange communication system.</p> <p style="text-align: justify;"><strong>Methods.&nbsp;</strong>Diagnostic tool &ldquo;Communication Matrix&rdquo;. Data collection was carried out through observation of the child in free and educational activities for one year, and conversation with parents. The study is presented by three diagnostic sections and their analysis.</p> <p style="text-align: justify;"><strong>Results</strong>. At the stage of primary diagnosis, the child&rsquo;s communicative characteristics were described and comments were given regarding the possibilities of taking them into account using the technique. Formed, partially formed and unformed communication skills of a child at the level of unintentional and intentional behavior, non-standard and standard communication, concrete and abstract symbols and language are identified. The objectives of correctional and developmental work are formulated based on a list of communication skills that are in the process of formation. The tasks were included in a special individual child development program and were implemented during the school day by a team of specialists, then reinforced at home with the participation of a private teacher and family members. At the final diagnostic stage, positive dynamics were noted in the development of communication at all levels. After a break (summer holidays), a regression of some skills was noted at the level of unintentional and intentional behavior, standard communication and specific symbols.&nbsp;</p> <p style="text-align: justify;"><strong>Conclusion.&nbsp;</strong>The &ldquo;Communication Matrix&rdquo; tool made it possible to conduct an initial diagnosis of the communication sphere of a child with a severe complicated form of autism and determine the tasks of correctional and developmental work. With the help of the instrument, changes in the child&rsquo;s communicative sphere were recorded during continuous correctional and developmental education and during a break from it. Also, during the work, the advantages and limitations of the technique in relation to a specific diagnostic case were highlighted.</p>